This invention relates to a luminosity probe for diesel-engine timing apparatus, and more particularly to a luminosity probe adapted to be mounted in a selected cylinder of a diesel engine.
The probe responds to the occurrence of combustion events in the cylinder by converting light into electrical signals which thereafter are processed in the timing apparatus. Additional details of timing apparatus incorporating such luminosity probe can be obtained by reference to U.S. Pat. No. 4,373,384, assigned to the assignee of this application.
A prior art luminosity probe is disclosed in appplication Ser. No. 285,942, filed July 23, 1981, now U.S. Pat. No. 4,441,021, assigned to the assignee of this application. The luminosity probe disclosed therein includes a tubular member having a portion adapted to be inserted in the opening of a selected cylinder of a diesel engine so as to be exposed to light occurring therein. The member has a portion that projects outside the cylinder. A light pipe is located in the member to transmit light therethrough. A coupler is telescoped with the projecting portion of the tubular member and houses a photodetector which converts the light traveling through the light pipe into electrical signals.
The light pipe is retained in the tubular member by epoxy or other binder. The light pipe being glass tends to have a very smooth surface. Certain luminosity probes are limited in the length of the bond line between the light pipe and the binder. As a result, the bond line may be inadequate, so that the light pipe can become dislodged from its optimal position.